Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: [Phys-l] sudden Vacuum freezing



On 05/07/2007 04:17 PM, Roger Haar wrote:

I understand what happened, but am amazed that the water was supercooled to a temperature such that so much water would freeze,

Yes, that's an impressive achievement. Freezing half the water
implies that the supercooled water must have been very, very
cold, if you think about the ratio of specific heat to latent
heat ... or, better, look at the enthalpy itself (since it
is not a straight line of the form heat capacity times T).
http://www.av8n.com/physics/phase-transition-heat.htm#fig-water-enthalpy

Here's the easy way to think about it: Look at the enthalpy
curve and figure out how much enthalpy you have to put in
to warm the water from (say) -40C to 0C. Then imagine
taking exactly that much enthalpy out at 0C, as the ice
forms.

Finding enough enthalpy to freeze half the water is not
easy, the way I read the chart.

The absolute limit is set by the temperature at which
homogeneous nucleation occurs. Wikipedia says the
limit is about -42C, and gives some references. That's
the conventional wisdom.

OTOH there are some theories and even some observations
that suggest water can be supercooled as far as -70C
i.e. a truly astonishing depth of supercooling. (This
may be restricted to very small droplets, I'm not
sure.)

===================

Understanding microscopically what is going on in a
supercooled liquid is a topic of current research.
Obviously it is far, far removed from ordinary
"textbook" thermodynamics, which is restricted to
thermal equilibrium.

Understanding anything having to do with H2O is always
super-extra-complicated.

On 05/07/2007 06:50 PM, Connie Tyree wrote:
.... Pick up a bottle and give it a slight shake or
slight squeez and watch the water to completely solid within seconds.

Completely? No liquid left over????

If you can do that reproducibly, it's worth publishing.
Seriously.